1. Field of the Invention
This invention relates in general to the construction of a breathing air humidifier for respirators and in particular to a humidifier which includes an inspiration conduit which has a foil surface of a material which is impervious to water but pervious to water vapor and which is in communication on its interior with the air being inspirated and on its exterior with heated water.
2. Description of the Prior Art
In an artificial respiration of patients by means of intubation and also during the spontaneous breathing a tracheotomized patient, the breathing air no longer passes through the laryngeal, nasal and pharyngeal cavities but passes directly into the bronchi. Since the laryngeal, nasal and pharyngeal cavities are no longer contacted by the breathing air this air can no longer be sufficiently warmed and humidified. The result is the drying up of the breathing air ways and the endangering of the function of the vibrating epithelium. In order to prevent the drying up of the breathing air ways or passages it is well known to provide breathing air humidifiers. The function of such a humidifier is to warm the inspiration air preferably up to the body temperature and at the same time to bring it to a relative humidity as high as possible preferably 100%. Almost all of the known breathing air humidifiers have the substantial drawback that the water evaporating therein increases the vacuum volume at the inspiration side. Due to the unavoidable impression under the inspiration pressure which may amount to 120 mm of water column, the inspiration volume difference between the respiration with and without water in the humidifier may amount to 20%. This for example in the respiration of infants is a very critical percentage difference.
Many types of breathing air humidifiers are known in the prior art:
With the so-called bubbler type the inspiration air is conducted through warmed water which humidifies the air. Entrained water droplets are retained by a granular matter provided above the water surface. The disadvantage of such bubblers is that the compressible volume varies with the volume of the water which is filled in. In addition the device is so bulky that it cannot be placed directly adjacent the patient's mouth. In long supply lines however the air tends to cool down. Consequently, a portion of the humidity contained in the inspiration air will condense. This condensate must be kept away from the patient by appropriate measures.
Humidifiers comprising a wick operated in a similar manner as the bubblers and as a surface humidifier has the disadvantage that the wick does not bring the air so intimately into contact with the water. The air flows past moistened wicks which take warmed water from a reservoir. Such humidifiers have the same drawbacks as the bubblers. However because they can be of smaller design it is possible to place them closer to the patient. The problems of condensation are therefore relatively more favorable but on the other hand it is more difficult to obtain a satisfactory humidification of the breathing air. Another air humidifier uses a hot vapor injection into the inspiration air stream. To produce the hot vapor the humidifier comprises a heated plate on which an adjustable quantity of water is evaporated. The water vapor which is produced passes into the inspiration air system and humidifies and warms the air. Air humidifiers of this kind can be constructed in a very small size. Thus condensation is no problem. The adjustment of the correct quantity of water for humidification of the air is very difficult. To small breathing air volumes may become overheated and too large a breathing air volume per minute may lead to an insufficient humidification and to a low temperature.